U.S. patent application number 13/019484 was filed with the patent office on 2012-08-02 for method for producing a watch case middle of reduced weight.
This patent application is currently assigned to RICHEMONT INTERNATIONAL SA. Invention is credited to Laurent CATALDO, Eli Liechty, Greg M. Morris.
Application Number | 20120192424 13/019484 |
Document ID | / |
Family ID | 45557962 |
Filed Date | 2012-08-02 |
United States Patent
Application |
20120192424 |
Kind Code |
A1 |
CATALDO; Laurent ; et
al. |
August 2, 2012 |
METHOD FOR PRODUCING A WATCH CASE MIDDLE OF REDUCED WEIGHT
Abstract
A method for producing a watch case middle having reduced weight
is disclosed. A 3-D data set is generated for the case middle, the
model comprising at least one internal cavity within the case
middle. The 3-D data set is converted into a plurality of layers,
each layer representing a cross-sectional layer of the middle, and
then the case middle is formed layer-by-layer from powdered
material using an additive manufacturing process such as DMLS in
order to provide the case middle with a unitary construction. Loose
powder is removed from each cavity via one or more powder
evacuation holes formed between the cavity and an external surface
of the case middle, and a through hole formed through the middle is
machined to a desired finish and/or precision, the through hole
being designed to receive a control member stem when a watch
movement is mounted inside the middle.
Inventors: |
CATALDO; Laurent; (Divonne,
FR) ; Morris; Greg M.; (Cincinnati, OH) ;
Liechty; Eli; (Maineville, OH) |
Assignee: |
RICHEMONT INTERNATIONAL SA
Villars-sur-Glane
CH
|
Family ID: |
45557962 |
Appl. No.: |
13/019484 |
Filed: |
February 2, 2011 |
Current U.S.
Class: |
29/896.33 |
Current CPC
Class: |
B33Y 80/00 20141201;
G04D 3/00 20130101; B33Y 40/00 20141201; B33Y 50/02 20141201; G04B
37/22 20130101; B29C 64/153 20170801; Y10T 29/49584 20150115; Y10T
29/49586 20150115 |
Class at
Publication: |
29/896.33 |
International
Class: |
G04D 99/00 20060101
G04D099/00 |
Claims
1. A method for producing a watch case middle having reduced
weight, comprising: generating a 3-D data set for the case middle,
the model comprising at least one internal cavity within the case
middle; converting the 3-D data set into a plurality of layers,
each layer representing a cross-sectional layer of the middle;
forming the case middle layer-by-layer from powdered material using
an additive manufacturing process in order to provide the case
middle with a unitary construction; removing loose powder from each
cavity via one or more powder evacuation holes formed between the
cavity and an external surface of the case middle; and machining a
through hole formed through the middle to a desired finish and/or
precision, the through hole being designed to receive a control
member stem when a watch movement is mounted inside the middle.
2. The method according to claim 1, wherein the case middle
comprises at least 25% less material than a solid middle having the
same external geometry but no internal cavities.
3. The method according to claim 1, wherein the case middle has an
outer peripheral surface and an inner peripheral surface defining a
generally cylindrical-shaped opening for housing the watch
movement, and the at least one internal cavity extend or extends
circularly around the middle between the inner and outer peripheral
surfaces.
4. The method according to claim 3, wherein the case middle further
includes two pairs lugs of projecting from the outer peripheral
surface, each pair of lugs being destined to receive an end of a
watch strap or bracelet, and the at least one internal cavity
further extending into the lugs.
5. The method according to claim 1, wherein the 3-D data set
includes an initial preformation of the through hole for receiving
the control member stem, the dimensions of the pre-formed through
hole in the 3-D data set being smaller than the final dimensions of
the through hole, the 3-D data set further including the formation
of walls surrounding the through hole.
6. The method according to claim 1, wherein the 3-D data set
includes solid cavity wall portions that extend throughout the
entire region of the middle in which the through hole for receiving
the control member stem is to be formed, and the through hole is
formed entirely during the step of machining the through hole.
7. The method according to claim 1, wherein the 3-D data set
includes a plurality of internal cavities within the case middle
and walls separating those cavities.
8. The method according to claim 1, wherein the 3-D data set
further includes support structures located within the at least one
internal cavity for strengthening the case middle.
9. The method according to claim 1, wherein the 3-D data set
includes the formation of the one or more powder evacuation
holes.
10. The method according to claim 1, wherein the one or more powder
evacuation holes are formed by machining said holes after the case
middle has been formed.
11. The method according to claim 1, wherein the one or more powder
evacuation holes are located in sites that remain hidden from view
when the case middle forms part of a fully assembled watch
case.
12. The method according to claim 1, further comprising, after the
step of removing loose powder, filling in the one or more powder
evacuation holes.
13. The method according to claim 1, wherein the layers have a
thickness in the range 1-100 .mu.m.
14. The method according to claim 1, wherein the additive
manufacturing process comprises direct metal laser sintering.
15. The method according to claim 1, wherein the additive
manufacturing process comprises an electron beam melting additive
manufacturing process.
16. The method according to claim 1, further comprising machining
areas of a bottom surface and a top surface of the case middle that
are respectively destined to receive a case back and a bezel of a
watch case.
17. The method according to claim 1, further comprising finishing
the external surface of the case middle.
18. The method according to claim 1, further comprising subjecting
the case middle to thermal treatment after removing loose powder
from each cavity and before machining the through hole to a desired
finish and/or precision.
19. The method according to claim 1, wherein the case middle is
formed layer-by-layer on a platform, and the method further
comprises separating the case middle from the platform after the
case middle has been formed.
20. A watch case middle comprising an outer peripheral surface and
an inner peripheral surface defining an opening for housing a watch
movement, the case middle comprising at least one internal cavity
that extends around the case middle between the inner and outer
peripheral surfaces such that the case middle comprises at least
25% less material than a solid case middle having the same external
geometry but no internal cavities, the case middle being formed
layer-by-layer from powdered material using an additive
manufacturing process such that the case middle has a unitary
construction throughout.
21. The case middle according to claim 20, wherein the powdered
material comprises a metal or pre-alloyed metal.
22. The case middle according to claim 20, wherein the powdered
metal material comprises a precious metal.
23. The case middle according to claim 20, wherein the case middle
further comprises support structures located within the at least
one internal cavity for strengthening the case middle.
24. A method for producing a watch case middle having reduced
weight, comprising: generating a 3-D data set for the case middle,
the model comprising at least one internal cavity within the case
middle and solid cavity wall portions that extend throughout the
entire region of the middle in which a through hole is to be
formed, the through hole being designed to receive a control member
stem when a watch movement is mounted inside the middle, converting
the 3-D data set into a plurality of layers, each layer
representing a cross-sectional layer of the middle; forming the
case middle layer-by-layer from powdered material using an additive
manufacturing process in order to provide the case middle with a
unitary construction; removing loose powder from each cavity via
one or more powder evacuation holes formed between the cavity and
an external surface of the case middle; and machining the through
hole through the solid cavity wall portions formed.
25. A method for producing a watch case middle having reduced
weight, comprising: generating a 3-D data set for the case middle,
the model comprising at least one internal cavity within the case
middle and the formation of one or more powder evacuation holes
between each cavity and an external surface of the case middle, the
powder evacuation holes being located in sites that remain hidden
from view when the case middle forms part of a fully assembled
watch case. converting the 3-D data set into a plurality of layers,
each layer representing a cross-sectional layer of the middle;
forming the case middle layer-by-layer from powdered material using
an additive manufacturing process in order to provide the case
middle with a unitary construction; removing loose powder from each
cavity via the one or more powder evacuation holes; and machining
the through hole through the solid cavity wall portions formed.
Description
FIELD OF INVENTION
[0001] The present invention relates to a method for producing a
watch case and in particular a watch case middle having reduced
weight.
BACKGROUND OF THE INVENTION
[0002] A watch case typically comprises four main components: a
middle, a crystal, a bezel surrounding the crystal fitted on top of
the middle, and a back fitted underneath the middle. The bezel and
the middle may in some cases be formed as a single piece, and the
middle also typically includes two pairs of projecting lugs that
enable the case to be attached to a watch strap or bracelet. The
case middle surrounds the watch movement. It is typically made from
solid metal material, and the middle is generally the most massive
of the watch case components by far.
[0003] In order to reduce the amount of material used in a watch
case and hence also the weight of the case and the cost of the
material used to produce it (particularly in the case of precious
metals), it has been proposed to hollow out the middle. For
example, EP626625 describes a precious metal watch case in which
the middle is formed by fitting a central cylindrical part and an
annular peripheral part together so that an annular cavity exists
between the two. In order to improve the strength of the middle, a
support frame in a non-precious metal is placed within the
cavity.
[0004] Similarly, in CH664251, a unitary bezel-middle having its
inner wall hollowed-out is fitted together with and fixes in place
a separate L-shaped encasing piece that itself holds the watch
movement. A hollow cavity exists between the bezel-middle and the
encasing piece.
[0005] Unfortunately, such prior art solutions for producing
hollowed-out watch case middles generally result in watch cases
that are of significantly reduced strength and that require complex
assembly. In addition, because the middle is not unitarily formed,
the watch case may suffer from reduced sealing or watertightness
compared to a conventional watch case. Furthermore, where a massive
middle is initially produced and then subsequently hollowed-out,
there may be a significant amount of material wasted that cannot be
readily reused.
[0006] There is consequently a need to provide a reduced weight
watch case and in particular a watch case middle for which the
above-mentioned shortcomings are alleviated.
BRIEF SUMMARY OF THE DISCLOSURE
[0007] The present invention addresses the above-described
disadvantages of the prior art by providing a method for producing
a watch case middle having reduced weight in which a 3-D data set
is generated for the case middle, the model comprising at least one
internal cavity within the case middle. The 3-D data set is
converted into a plurality of layers, each layer representing a
cross-sectional layer of the middle, and then the case middle is
formed layer-by-layer from powdered material using an additive
manufacturing process such as DMLS in order to provide the case
middle with a unitary construction. Loose powder is removed from
each cavity via one or more powder evacuation holes formed between
the cavity and an external surface of the case middle, and a
through hole formed through the middle is machined to a desired
finish and/or precision, the through hole being designed to receive
a control member stem when a watch movement is mounted inside the
middle.
[0008] The present invention further provides a watch case middle
comprising an outer peripheral surface and an inner peripheral
surface defining an opening for housing a watch movement, in which
the case middle comprises at least one internal cavity that extends
around the case middle between the inner and outer peripheral
surfaces such that the case middle comprises at least 25% less
material than a solid case middle having the same external geometry
but no internal cavities. The case middle is formed layer-by-layer
from powdered material using an additive manufacturing process such
that the case middle has a unitary construction throughout.
[0009] These and other embodiments and variations are described
further below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The objects and advantages of the present invention will be
better understood and more readily apparent when considered in
conjunction with the following detailed description and
accompanying drawings which illustrate, by way of example,
preferred embodiments of the invention and in which:
[0011] FIG. 1 is a perspective view of a watch case middle produced
in accordance with the method of the present invention;
[0012] FIG. 2 is a perspective section view taken along the plane
II-II in FIG. 1 looking downward toward the back of the case middle
in one embodiment;
[0013] FIG. 3 is a perspective section view taken along the line
III-III in FIG. 2;
[0014] FIG. 4 is a perspective section view taken along the line
IV-IV in FIG. 2;
[0015] FIG. 5 is a perspective section view taken along the line
V-V in FIG. 2;
[0016] FIG. 6 is a perspective section view taken along the line
VI-VI in FIG. 2;
[0017] FIG. 7 is a perspective section view taken along the line
VII-VII in FIG. 2;
[0018] FIG. 8 is a flow diagram illustrating a method for producing
a watch case middle in accordance with an embodiment of the
invention;
[0019] FIG. 9 is a perspective section view taken along the plane
II-II in FIG. 1 looking downward toward the back of the case middle
in another embodiment; and
[0020] FIG. 10 is a diagram of an exemplary additive manufacturing
machine suitable for use in the method of FIG. 8.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0021] FIG. 1 is a perspective view of an exemplary watch case
middle 10 produced in accordance with the method of the present
invention. Middle 10 has an outer peripheral surface 12, which in
this example has four slightly rounded sides, and an inner
peripheral surface 14 defining a generally cylindrical-shaped
opening 16 in which a watch movement (not shown) can be housed. In
known manner, the profile of inner peripheral surface 14 includes a
series of projections and grooves for securely holding the watch
movement cage. Middle 12 further has a bottom surface 20 onto which
a watch case back (not shown) can be fitted, and a top surface 22.
Top surface 22 includes profiled surface areas 22 and 24 that
include a series of channels and flange-like projections. The
latter are designed to receive and fit a bezel and a glass crystal
in conventional manner; again neither the bezel nor the crystal is
shown in the drawings. Sealing joints such as O-rings are generally
interposed between the middle 10 and each of the other components
of the watch case during assembly.
[0022] Case middle 10 further includes two pairs of projecting lugs
30, with each pair being destined to receive an end of a watch
strap or bracelet. Each lug 30 has a hole 32 for fixing the end of
the bracelet to the lugs by any suitable manner, for example using
a bar and screws. It will however be appreciated that in some
bracelet-fastening systems, no holes are needed to secure a
bracelet to a watch case.
[0023] On one side of outer surface 12, a through hole 40 for
receiving the stem of a watch control member notably a setting
crown (not shown) extends through the middle 10 into cavity 16. A
similar through hole 42 (FIG. 2) extends through the middle and is
designed to receive the stem of a pusher button (not shown). In the
illustrated example of FIG. 1, the surface 12 also includes two
indentations 46, on each side of through hole 40, for receiving the
feet of a crown-covering bridge (not shown) such as the well-known
bridge used in Panerai Luminor.RTM. watches. Within the
indentations 46, blind threaded holes 44 are formed to receive
screws that will fix the crown-covering bridge to case middle 10
after the crown control member has been mounted.
[0024] Case middle 10, though formed in a unitary manner, has at
least one internal cavity 50 formed within it. As noted above,
depending on the size of the cavity or cavities, the weight of the
case middle and the amount of material it contains can be greatly
reduced. Preferably case middle 10 comprises at least 25% less
material (and hence weighs at least 25% less) than a solid middle
having the same external geometry but no internal cavities. More
preferably, the reduction in weight and amount of material used for
the middle is at least 40%. As described in more detail below in
connection with FIG. 8, this reduction is achieved by building the
case middle 10, using an additive manufacturing process in which an
energy source is used to unify, i.e., solidify or bond, layers of
powdered material to one on top of another.
[0025] While the method of the present invention is particularly
applicable to watch cases made from metals and alloys thereof, it
may also be used to produce watch cases from any powdered material
(for example powders for ceramics or elastomers) that can be fused,
melted or otherwise united together by way of an additive
manufacturing process. The method is especially advantageous for
producing cases made of metals that are relatively heavy (such as
stainless steel) and/or expensive (such as gold and platinum).
Other watch case powdered materials such as Cobalt Chromium and
Titanium alloys may also be used.
[0026] FIGS. 2-7 illustrate the internal geometry of case middle
10. More particularly, FIG. 2 is a perspective section view taken
along the plane II-II in FIG. 1 looking downward toward the back
side 2- of the case middle according to one embodiment. FIGS. 3-7
are perspective section views taken respectively along the lines
III-III, IV-IV, V-V, VI-VI, and VII-VII in FIG. 2. As shown, middle
10 is formed throughout by walls 52 that have been unitarily
formed, layer by layer, from one or more desired powdered
materials. Walls 52 define at least one internal cavity while also
surrounding holes 40, 42, 44 and 32 that are formed through or
within the case middle. (It should be noted that although the
location of bracelet fixation through holes 32 is shown for clarity
in FIG. 2, they do not lie in the section plane II-II.)
[0027] In the illustrated embodiment, case middle 10 comprises a
single contiguous internal cavity 50 that generally extends
circularly around the middle between surfaces 12 and 14 as well as
into lugs 30. The internal shape and geometry of the cavity can
vary depending on the external profile of the case middle and the
thickness of walls 52. The latter depends, in turn, partly on the
type of powder material used and the strength of the resulting
unified material. For each cavity, at least one powder evacuation
hole 60, 62 is also formed in order to enable excess or loose
powder to be removed from the cavity after the building of the
layers is complete. In the illustrated embodiment, three such
powder evacuation holes 60 are formed between the bottom surface 20
of middle 10 (which receives the watch case back) and the cavity
50. A further powder evacuation hole 62 (FIG. 1) is formed between
the top surface 22 of middle 10 (more particularly the area 24 of
surface 22 that receives the bezel) and the cavity 50. The purpose
and role of holes 60, 62 are described further below.
[0028] Referring now to the flow diagram of FIG. 8, a method for
producing a watch case middle in accordance with a preferred
embodiment of the invention is now described. At a first step 80, a
three-dimensional (3-D) data set of the watch case middle 10 is
generated based on its desired physical parameters, in particular
the shapes and sizes of the surfaces 12, 14, 20, and 22 and the
location of holes 40, 42, 44 and 32. As is well known, 3-D
computer-aided-design (CAD) data models can be generated using
programs such as SolidWorks.RTM.. In other cases, a data modeling
tool specific to the additive manufacturing process and/or machine
being used to form case middle 10 may be used. Such a tool may
notably convert a CAD data model to a data set format suitable for
use by the additive manufacturing machine. Whatever the form, the
3-D data set for watch middle 10 notably models the configuration
of internal cavity 50, including the material that forming the
cavity walls 52 that surround control member stem through holes 40
and 42, screw holes 44, and bracelet fixation holes 32. Where the
middle includes several non-contiguous internal cavities, the
cavity walls separating each of these are also included in the
model.
[0029] Optionally, the 3-D data set may include from the outset the
formation of holes 40, 42, 44 and 32; in this case, as described
further below, these holes are designed in the data model to have
slightly smaller dimensions than what is finally desired.
Alternatively, the 3-D data set can include thicker solid cavity
wall portions 52 that extend throughout the entire region of the
middle in which holes 40, 42, 44 and 32 are to be formed, and those
holes are then formed entirely during a subsequent machining step,
after to the layer-by-layer building of middle 10. In a similar
manner, powder evacuation holes 60 and 62 may be formed initially
as part of the 3-D data set information (e.g., by modifying a CAD
data model to account for them), or they may alternatively be
formed as part of a post-machining step.
[0030] In an alternative embodiment of a case middle 10'
illustrated in FIG. 9, the cavity 50 may further include a support
structures 54 in order to strengthen case middle 10. FIG. 9 is a
perspective section view taken along the plane II-II in FIG. 1, and
apart from the presence of support structures 54, case middle 10'
of FIG. 9 is essentially identical to case middle 10 of FIG. 2. In
the example of FIG. 9, the support structures 54 are pillar-like
elements disposed throughout cavity 50, each extending from the
bottom of case middle to the top. In general, however, support
structures may be arranged and may extend in any structurally
appropriate manner. For example, internal cavity support structures
may have a grid-like arrangement or they may extend in parallel to
the plane II-II similar to beams. Support structures may especially
be desirable where the cavity walls 52 are designed to be very
thin. Where support structures 54 are built within the cavity of
the case middle, they are included in the 3-D data set at step
80.
[0031] It will be appreciated that the additive manufacturing
machine or a related tool may, for example, automatically determine
the location, size, and geometry for the support structures 54
and/or powder evacuation holes 60, 62 based on a set of criteria or
instruction input by a user. In this case, the additive
manufacturing machine or tool can automatically supplement and
modify the initial user-specified data for the middle to generate a
final 3-D data set to be used in the additive manufacturing process
as described below. More generally, the generation of a 3-D data
set that includes all of the above described features in a manner
that optimizes both weight reduction and structural integrity
generally depends on a number of factors including the shape of the
case middle and its various parts, the type of powder material used
and the strength of the resulting unitary material. At the same
time, the flexibility of additive manufacturing processes enables
any specific area of the case middle geometry to be reinforced
without changing the middle's overall design. For example, if it is
determined that there is a weak areas in a specific section of a
wall, that section of the wall can be made thicker or an
appropriate support structure can be readily added in.
[0032] Once the 3-D data set for middle 10 is fully generated, it
is converted at step 82 into a plurality of layers, each layer
representing a cross-sectional layer of the middle. These layers
will be formed one onto the other using an additive manufacturing
machine and process described below, and the conversion is
typically carried out by the additive manufacturing machine or a
related software tool thereof. Preferably, this conversion occurs
so that the layers run in parallel manner along an axis
perpendicular to the face of the watch (i.e., to plane II-II),
extending from the bottom surface 20 to the top surface 22. The
layers preferably have a thickness in the range 1-100 .mu.m, and
they may be of equal thickness or different thicknesses. For
example, for a watch case middle having a height of approximately 1
cm, and using a uniform layer thickness of 20 .mu.m, the 3-D data
set would be converted into around 500 layers.
[0033] As shown at step 84, case middle 10 is formed layer-by-layer
using an additive manufacturing process (also sometime called a
rapid manufacturing process). In this type of process, an energy
source such as a laser or an electron beam is used to unite (i.e.,
to solidify, fuse or bond) layers of powdered material together.
For example, laser-based additive manufacturing is accomplished by
directing a high power laser at a substrate or platform to create a
melt pool. In particular, the direct metal laser sintering (DMLS)
process, which was developed by EOS GmbH in Germany and is designed
to sinter or fuse pre-alloyed powdered metals, is particularly
suitable for producing metal watch case middles in accordance with
the present invention. In DMLS, each layer is formed by depositing
a uniformly thick layer of powdered material across an entire build
area. The powder in specific areas is then selectively melted by
the laser so that those areas fuse to the immediately preceding
layer of fused material (that is present in solid form underneath
the powder layer). Additional information on additive manufacturing
is found in the "Wohlers Report 2010--Additive Manufacturing State
of the Industry", Annual Worldwide Progress Report, Terry Wohlers,
ISBN 0-9754429-6-1, the contents of which are incorporated herein
by reference.
[0034] FIG. 10 is a diagram illustrating the main parts of a DMLS
machine 100, such as the EOSINT M270 machine from EOS GmbH,
suitable for building case middle 10. As shown, machine 100
includes a building platform 110 onto which the case middle is
manufactured. Platform 110 can be successively lowered as the
fusing of powder to produce each layer is completed. In this
manner, the building of each layer occurs at the same vertical
position within machine 100. A powder reservoir 120 cooperates with
a dispenser platform 130 and a recoating system 140 to evenly
dispense metal powder during the building/processing of each layer.
The energy source module includes a laser 150, a series of mirrors
160, and a galvanometer-scanner with f-Theta lens 170 and is
precisely controlled in response to the final 3-D data set that is
used by the machine's control system 180.
[0035] More generally however, while a DMLS machine 100 is shown,
any suitable additive manufacturing process that directs an energy
source to unite, i.e., solidify or bond, layers of powdered
material together to provide a unitary case middle construction may
be used. For example, case middle 10 may also be built using an
electron beam melting (EBM) or an ultrasonic consolidation (UC)
additive manufacturing process.
[0036] If powder evacuation holes 60 and 62 were included in the
final 3-D data set and therefore were formed during additive
manufacturing at step 84, then, at step 86, loose powder remaining
in each cavity is removed via the one or more powder evacuation
holes 60, 62 formed between that cavity and an external surface of
the middle. This may be accomplished in different manners; for
example by using suction or by blowing into a first powder
evacuation hole so that powder exits from a second powder
evacuation hole. On the other hand, if the powder evacuation holes
were not included in the 3-D data set, then they may be formed by a
machining step once the additive manufacturing at step 84 is
complete.
[0037] It will be appreciated that the powder evacuation holes are
preferably in locations that will subsequently be covered and
sealed by other components of the watch case, e.g., on an area of
surface 20 that will be covered by the watch back and/or an area of
surface 22 that will receive the bezel. Holes 60, 62 may also be
subsequently filled in after removing powder in order to eliminate
the possibility of any remaining loose powder interfering with the
watch mechanisms and/or to prevent the powder from possibly
affecting the robustness of the case middle. Holes 60, 62 may be
filled by, for example, welding the hole shut. However, even when
filled, it is preferred that the powder evacuation hole sites
remain hidden when the watch case is finally assembled.
[0038] At step 88, a thermal treatment step is next preferably
carried out on the case middle. The duration and temperature of the
thermal treatment may vary depending on the nature of the powdered
material. This step may provide stress relief within the case
middle structure as well as other potential structural benefits.
However, stress relief may not be necessary in some instances or it
may be achieved by alternative means, for instance using vibratory
stress relief. Case middle 10 may also at this stage be separated,
e.g. mechanically, from the platform 110 of machine 10. However,
separation could alternatively occur prior to the loose powder
removal step or at a later stage.
[0039] Subsequently, at step 90, holes 40, 42, 44, and 32 are
machined to obtain a desired surface finish and/or precision
throughout the holes. As indicated above, holes 40, 42, 44, and 32
may be completely formed using conventional machining tools at this
step 90, in which case the 3-D data set includes thick cavity wall
portions 52 that extend throughout the entire region of the middle
in which holes 40, 42, 44 and 32 are to be formed. Alternatively,
the 3-D data set may include an initial pre-form of holes 40, 42,
44 and 32, but where they are designed to have slightly smaller
dimensions than those that are ultimately necessary in the final
case middle 10. In this case, the machining step at 90 is still
carried out to arrive at the desired surface finish and/or
precision throughout holes 40, 42, 44 and 32. The former option may
be preferred especially when hard materials are used, since
drilling or milling through an already existing hole (as opposed to
solid material) may cause tools to fail prematurely. With respect
to the latter option, although it is envisaged that in the future
additive manufacturing processes will enable the thickness of the
layers to be reduced and hence for a better overall precision of
the features of case middle to be achieved, it is believed that the
ability of the additive manufacturing process to finely control
surface finish (i.e., roughness) and/or surface roundness will
remain inferior to what can be achieved using machining tools.
[0040] Additional precision machining steps are also preferably
carried out on the areas of surfaces 20 and 22 destined to receive
the back and the bezel of the watch case. Lastly, a final step of
finishing (e.g., polishing) the external surface of the middle--or
at least that part that will remain visible once the watch is fully
assembled--is carried out prior to assembling the watch case.
[0041] In this manner, a watch case middle produced by the method
of the present invention continues to have a strong, resilient and
unitary construction despite using less material and having a
significantly reduced weight. In known manner, the middle can
subsequently be used with a case back, bezel and crystal to
assemble a watch case that houses a watch movement. As a further
advantage, the method of the present invention greatly facilitates
the construction of watch case middles having varied and complex
geometries. Moreover, the method may also be adapted to produce
other light-weight external watch components; in particular
bracelet links that are conventionally made of solid metal but that
could instead be produced with an internal cavity using an additive
manufacturing process.
[0042] While the invention has been described in conjunction with
specific embodiments, it is evident that numerous alternatives,
modifications, and variations will be apparent to those skilled in
the art in light of the foregoing description.
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